1. Field of the Invention
The subject invention is directed to a paging device which tells the user whether he or she is in range of the paging transmitter and, more particularly, to a paging device which checks the carrier signal strength and provides the user with an aural, visual, or tactile output if the paging device is in range of the transmitter. Another aspect of the invention is the provision in a paging device which allows the user to monitor the error rate of decoded messages and thereby monitor the performance of the device at a given location.
2. Description of the Prior Art
Paging devices are in common use by professionals, executives, and many others in virtually all urban and many suburban areas. In a standard paging system, a signal is transmitted from a transmitter to alert a person with a paging device that his or her office or similar base station wishes to communicate with them. The transmitted signal is received by the paging device and identified as being intended for that particular device. An alerting signal is generated which indicates to the user that he or she is being paged.
In ordinary paging devices, a user cannot tell if he or she is out of range of the paging transmitter or shielded from the paging transmitter and, as a result, missing urgent and important communications. A sophisticated user who might suspect such a possibility, might go to a pay telephone and try calling him or herself to see if the pager is activated. This, however, has limitations as the user is only able to confirm an in range or out of range condition at the location of the pay telephone but generally not at the location where he or she is most likely to be. The alternative is to call in to the head office at regular intervals to get his or her messages, but this defeats the purpose of the pager.
An example of a commercially available paging device is Motorola's "Pagecom" radio pager, and there are many others. In the patent literature, U.S. Pat. No. 3,911,416 to Feder and assigned to Motorola describes a silent call pager that produces a vibratory alerting signal when the paging signal is received. Ishii in U.S. Pat. No. 4,462,030 describes an audible annunciator with an alarm lamp for a paging device. U.S. Pat. Nos. 4,019,142 to Wycoff and 4,431,990 to Wycoff et al. disclose selective call communication receivers for use in paging systems. None of these, however, contemplate any means for detecting whether a paging device is out of range of the transmitter and alerting the user of that fact.
Also known in the prior art are voice message pagers which alert the user with an audible voice message. Such pagers typically have a squelch circuit that operates to prevent any audible output except for those messages which are identified as for that pager. A sophisticated user of such a voice message pager might open the squelch in an effort to monitor the channel activity. But even if the thought occurred to such a sophisticated user, which is unlikely, it would be difficult to accurately judge the quality of the signal.
More recently, pagers have been implemented using microprocessors so that many of the functions that were previously hardwired into the device are now controlled by the microprocessor under software or firmware control. Typically, the microprocessor is used to perform the decoding and logic functions which were previously performed by discrete logic circuits. This results in a simplification of the circuitry by reducing the chip count on the pager printed circuit board, but at the same time introduces an increased level of sophistication by permitting more complex functions to be programmed. A specific example is the ability to provide error detection and correction. Examples of pagers using microprocessors in decoding functions are U.S. Pat. Nos. 4,383,257 to Giallanza et al., 4,384,361 to Masaki, 4,438,433 to Smoot et al., 4,536,761 to Tsunoda et al., 4,613,859 to Mori, 4,642,632 to Ohyagi et al., and 4,682,148 to Ichikawa et al.
It is known in diverse arts to provide signal strength measurement or range detecting capabilities. For example, U.S. Pat. No. 4,032,723 to Mendoza discloses a cordless telephone system which provides an "out-of-range" indicator on the mobile telephone and, if desired, on the base station. The indicator signals that the telephone is at a range in excess of the operating capability of the system. The Mendoza cordless telephone is specifically useful when walking from room to room in a house and at no time more than a short distance from the base station.
U.S. Pat. No. 4,675,656 to Narcisse discloses an out of range personnel monitor and alarm. The device alerts an attendant that a supervised person has walked beyond a predetermined prescribed distance. U.S. Pat. No. 4,661,996 to Scandurra discloses a method for indicating radio frequency carrier loss in remotely controlled vehicles. More specifically, circuitry is provided on a remotely controlled airplane which determines the loss of a carrier and therefore the loss of remote control. U.S. Pat. No. 4,060,767 to Lohrmann discloses a self test circuit for multichannel radio receivers which reports to the operator whether or not the receiver is sensitive to receive signals within a plurality of channels.
The problem of missing urgent and important calls because a paging device is either out of range of the transmitter or shielded from the transmitter has not been addressed in the prior art. The problem is particularly acute in the very environment where pagers are most used, that is, cities where buildings and population are most dense. The user of a pager in this environment naturally assumes that as long as he or she is within the city, they will receive all pages. However, due to shielding by buildings and other structures, this may not be the case. In fact, even within the same room there may be variations in sensitivity in different locations which could make the difference between receiving and missing a page.